package/libnss: fix build on ARM big endian

package/libnss: fix build on ARM big endian

Fix the follownig build failure on ARM big endian raised since bump to
version 3.68 in commit 0a73b9b962421ce7a72c88e5f5bbd8849f21b041:

Linux2.6_aarch64_aarch64_be-linux-gnu-gcc_glibc_PTH_64_DBG.OBJ/Linux_SINGLE_SHLIB/sha256-armv8.o: In function `SHA256_Compress_Native':
sha256-armv8.c:(.text.SHA256_Compress_Native+0x0): multiple definition of `SHA256_Compress_Native'
Linux2.6_aarch64_aarch64_be-linux-gnu-gcc_glibc_PTH_64_DBG.OBJ/Linux_SINGLE_SHLIB/sha512.o:sha512.c:(.text.SHA256_Compress_Native+0x0): first defined here
Linux2.6_aarch64_aarch64_be-linux-gnu-gcc_glibc_PTH_64_DBG.OBJ/Linux_SINGLE_SHLIB/sha256-armv8.o: In function `SHA256_Update_Native':
sha256-armv8.c:(.text.SHA256_Update_Native+0x0): multiple definition of `SHA256_Update_Native'
Linux2.6_aarch64_aarch64_be-linux-gnu-gcc_glibc_PTH_64_DBG.OBJ/Linux_SINGLE_SHLIB/sha512.o:sha512.c:(.text.SHA256_Update_Native+0x0): first defined here

Fixes:
 - http://autobuild.buildroot.org/results/237aba0c16a34fec1b0fe50fe08cace438eda1bf

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>